This application is based on application No. 2000-270068 filed in Japan, the content of which is hereby incorporated by reference.
The present invention relates to a method of manufacturing a micro glass optical element such as a collimator lens for optical communication, an optical pickup lens and an endoscope lens and a micro glass droplet for manufacturing a micro glass optical element, and a micro glass optical element and a glass material for molding obtained by the method.
Micro glass optical elements used to be manufactured by grinding. However, since this method is inferior in productivity, the following methods have been used in recent years:
(A) Method of heating a glass material having an approximate shape, and pressing it with a mold;
(B) Method of dropping a molten glass droplet onto a heated mold, and pressing it; and
(C) Method of solidifying a molten glass droplet by cooling, thereby manufacturing a spherical lens.
However, in manufacturing a micro optical element with a diameter of, for example, approximately xcfx860.5 to xcfx863 mm, these methods present the following problems:
In the case of the method (A), it is necessary to prepare a micro glass material for molding having a corresponding volume, and since it is difficult to process such a micro glass material, cost increases. Another method for obtaining a micro glass material is machining glass material molded so as to have a larger volume, into a micro glass material. In this method, cost also increases because the number of manufacturing steps increases.
In the case of the method (B), it is difficult to obtain a micro molten glass droplet with a diameter of not more than xcfx863 mm for the following reason: Normally, the weight of a glass droplet dropped from a nozzle is represented by the following expression:
mg=2xcfx80rYxe2x80x83xe2x80x83(1) 
Here, m is the mass of the glass droplet;
g is the acceleration of gravity;
r is one-half the outside diameter of the nozzle tip; and
Y is the surface tension of the glass droplet.
According to the expression (1), the weight of the glass droplet can be reduced by reducing the outside diameter of the nozzle tip. In actuality, however, 1) since it is necessary for the nozzle to have a predetermined inside diameter in order for molten glass to flow through the nozzle, the reduction in the outside diameter is limited, and 2) since molten glass wets and spreads at the nozzle tip to increase the apparent outside diameter of the nozzle tip, the reduction in the outside diameter produces no effect. Thus, in actuality, it is difficult to obtain a molten glass droplet having a size of a certain degree or smaller, and the lower limit of the diameter of the molten glass droplet is xcfx863 mm.
In the case of the method (C), like in the case of the method (B), it is difficult to obtain a micro glass droplet with a diameter of not more than xcfx863 mm.
A glass droplet with a diameter of not less than approximately xcfx863 mm can be obtained by dropping molten glass from a nozzle as usually performed. However, in that case, to adjust the weight of the glass droplet, it is normally necessary to change the outside diameter and the shape of the nozzle, so that the rate of operation of the production facilities decreases. This is a big factor of cost increase.
An object of the present invention is to provide an improved method for obtaining a micro glass droplet by solving the problems of the methods (A) to (C).
An object of the present invention is, particularly, to provide a method for obtaining a micro glass droplet with a diameter of not more than xcfx863 mm.
Another object of the present invention is to provide a method for adjusting the size of the glass droplet easily and precisely without changing the nozzle.
The present invention relates to a method of manufacturing a micro molten glass droplet with a diameter of not more than 5 mm, characterized in that by colliding a molten glass droplet with a micro through hole formed in a plate-shaped member, at least part of the glass droplet is pushed out to the reverse surface of the micro through hole as a micro droplet.
Particularly, the present invention relates to the above-described manufacturing method wherein the collision of the molten glass droplet is by a free fall of the molten glass droplet dropped from a nozzle.
Moreover, the present invention relates to a method of manufacturing a micro spherical lens or a micro spherical material for pressing, wherein a micro molten glass droplet obtained by any of the above-described methods is solidified by cooling.
Further, the present invention relates to a micro optical element manufactured by dropping a micro molten glass droplet obtained by any of the above-described methods onto a mold and molding it, or to a glass material for pressing manufactured by dropping a micro molten glass droplet obtained by any of the above-described methods onto a mold and preliminarily molding it.
Further, the present invention relates to a method of adjusting the weight of a micro molten glass droplet in any of the above-described methods of manufacturing a micro molten glass droplet, wherein the adjustment is made by adjusting any or all of the diameter of the micro through hole, the distance from the nozzle to the micro through hole and the temperature of the molten glass.
In addition, the present invention relates to an apparatus for manufacturing a micro molten glass droplet with a diameter of not more than 5 mm, including a nozzle, and a plate-shaped member placed below the nozzle and having a micro through hole for further dropping at least part of a molten glass droplet dropped from a nozzle.